Wideband cable system

ABSTRACT

A wideband cable modem system increases available bandwidth of a single channel by encoding a data stream into wideband packets. The wideband packets are associated with a logical wideband channel that extends over multiple physical downstream cable channels.

BACKGROUND

[0001] The Data Over Cable Service Interface Specification (DOCSIS)standard defines a high speed, bi-directional, data communicationchannel between cable providers and cable customers. The DOCSIS standarddefines the layer 1 thru layer 3 communication protocols, timings, andRadio Frequency (RF) specifications for data traffic over cable systems.The communication media can be either coaxial cable or fiber.

[0002]FIG. 1 shows how Internet Protocol (IP) traffic is currentlytransferred over a DOCSIS system. A communication link is establishedbetween a Cable Modem Termination Systems (CMTS) 14 on the cableprovider end and a Cable Modem (CM) 20 on the customer premises. Datatransfers from the CMTS 14 to the CM 20 are referred to as downstreamwhile transfers from the CM 20 to the CMTS 14 are referred to asupstream.

[0003] The CMTS 14 at a cable system headend may include a Wide AreaNetwork connection 12, such as an Ethernet connection, that receives IPtraffic. Other types of network interfaces may also be used such asDynamic Packet Transport/Resilient Packet Ring (DPT/RPR) orPacket-over-SONET/SDH (POS) The CMTS 14 modulates the IP traffic over asingle downstream channel 16 on a high speed Hybrid Fiber Coax (HFC) 19.In one instance, the single downstream channel 16 has a bandwidth limitof about 30 to 42 Million Bits Per Second (Mbps) and may supplydownstream IP connectivity for up to 8000 different cable modems 20connected to the same cable plant 19. Each cable modem 20 demodulatesthe downstream traffic and formats the traffic for transfer overEthernet link 22. Upstream IP traffic is transferred over upstreamchannel 18.

[0004] Most cable traffic consists of data flowing in the downstreamdirection from CMTS 14 to CM 20. Current bandwidth may be sufficient forlarge numbers of cable modems with bursty traffic that can operateefficiently on shared bandwidth. However, current cable systems cannotsupport applications that have a high average bandwidth such as ConstantBit Rate (CBR) or Variable Bit Rate (VBR) Video.

[0005] The present invention addresses this and other problemsassociated with the prior art.

SUMMARY OF THE INVENTION

[0006] A wideband cable modem system increases available bandwidth of asingle channel by encoding a data stream into wideband packets. Thewideband packets are associated with a logical wideband channel thatextends over multiple downstream physical cable channels.

[0007] The foregoing and other objects, features and advantages of theinvention will become more readily apparent from the following detaileddescription of a preferred embodiment of the invention which proceedswith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a background diagram showing downstream and upstreamchannel used in a cable plant for transferring IP data.

[0009]FIG. 2 is a block diagram showing how a wideband cable system usesmultiple downstream channels for carrying downstream IP traffic.

[0010]FIG. 3 is a detailed diagram of the circuitry used in a widebandcable system.

[0011]FIG. 4 shows MPEG packet ordering in a wideband channel.

[0012] FIGS. 5-9 show different fields in a wideband packet.

[0013]FIGS. 10 and 11 show how wideband channels are dynamically changedover different RF channels.

[0014] FIGS. 12-14 show how different wideband and narrowband channelsare associated with different RF channels.

[0015]FIG. 15 shows how DOCSIS MAC frames can span wideband packets.

[0016]FIG. 16 shows one example of how bytes are striped over multipleRF channels.

[0017]FIG. 17 shows a wideband channel descriptor.

[0018]FIG. 18 is a block diagram showing how the wideband cable systemis configured.

DETAILED DESCRIPTION

[0019] Referring to FIG. 2, a group of downstream RF channels 30 in anHFC 33 are bundled together into one wideband channel 35. A single RFchannel 30 is defined in the nomenclature of the present invention as aNarrowBand (NB) channel. The wideband channel 35 is a logical channelthat spans one or more physical RF channels 30.

[0020] An IP server 26 outputs an IP data stream to a Wideband CableModem Termination System (WCMTS) 28 over an Ethernet connection 27 orsome other type of Wide Area Network (WAN) link. Any type of data can besent over connection 27, but in one example a video data stream is sent.The WCMTS 28 transmits portions of the data stream over the multipledifferent downstream RF channels 30.

[0021] The wideband channel 35 contains a number of wideband transportsub-channels which can be dynamically adjusted for varying bandwidthrequirements. Legacy protocols can be interlaced into the widebandchannel maintaining backward compatibility with existing cable modems.The bandwidth of the wideband channel 35 provides scalable and efficientVariable Bit Rate (VBR) utilization of data/voice/video IP streams in aDOCSIS compatible environment.

[0022] The individual downstream RF channels 30 are received at one ormore Wideband Cable Modems (WCMs) 34 on the HFC plant 33. In oneembodiment, the WCMTS 28 also operates as a conventional CMTS 14(FIG. 1) and the WCMs 34 also operate as conventional CMs 20 as shown inFIG. 1. An upstream channel 32 is used for upstream DOCSIScommunications from the WCMs 34 to the WCMTS 28.

[0023] The RF channels 30 are independent of each other. All RF channels30 could originate from a single multi-channel WCMTS 28, but eachdifferent RF channels may go to different WCMs 34. Many WCMs 34 canshare a single or multiple downstream RF channels 30. Data istransmitted via the RF channels 30 by framing DOCSIS MAC frames intoMotion Picture Experts Group—Transport Stream (MPEG-TS) packets.

[0024] The WCMs 34 can simultaneously demodulate each of the differentchannels 30 and regenerate the different portions of the original datastream received on link 27. In one example, the different portions ofthe data stream distributed over the different downstream RF channels 30are reformatted back into Ethernet frames and sent over link 36 to an IPSet Top Box (STB) 38. The STB 38 converts the digital data contained inthe Ethernet frames into an analog signal for displaying on a television40.

[0025]FIG. 3 shows the circuitry in the WCMTS 28 and the WCM 34 thatencode and decode the wideband channel 35. The WCMTS 28 includes abackplane 42 that couples data from the WAN connection 27 to a widebandtransmit framer 44 and a Media Access Control (MAC) interface 46. In oneembodiment, the wideband framer 44 separates Ethernet frames intowideband packets that are transmitted simultaneously over the multipledownstream channels 30.

[0026] In one example, the wideband channels 30 are each modulated usingQuadrature Amplitude Modulation (QAM). In one example, 64 QAM modulationwith 16 downstream RF channels 30 provides approximately 480 Millionbits per second (Mbps) of downstream bandwidth. Using 256 QAM modulationprovides approximately 640 Mbps of downstream bandwidth. Each downstreamRF channel 30 is associated with a Quadrature Amplitude Modulator (QAM)and Up-Converter (U) 48. The Q&U's 48 each modulate the MPEG digitaldata over a different RF channel.

[0027] The MAC interface 46 is also used for transmitting DOCSIS IP dataover a single RF channel 30A and receiving DOCSIS IP data over upstreamRF channel 32. A demodulator 50 demodulates upstream IP traffic receivedover upstream channel 32. The MAC 46 in the WCMTS 28 can use the sameQ&U 48A for transmitting narrowband traffic, wideband traffic, or bothnarrowband and wideband traffic over downstream channel 30A.

[0028] Each WCM 34 includes a wideband tuner 54 that includes multipleTuners (T) and QAM demodulators (D) 56. The T&Ds 56 demodulate thedigital data from the downstream channels 30. A wideband Receive (Rx)framer 58 reassembles data received over the different RF channels 30into the data stream originally sent by the server 26 (FIG. 2).

[0029] A decoder 60 includes a DOCSIS MAC/PHY interface for controllinghow MPEG frames are reassembled into Ethernet frames and sent over theEthernet link 36. The MAC/PHY interface is also used for sending IP dataover upstream RF channel 32 to the MAC interface 46 in CMTS 14. The MACinterface 46 in the WCMTS 28 sends a Wideband Channel Descriptor (WCD)55 to the WCMs 34 that indicate which RF channels 30 are part of thewideband channel 35.

[0030] Wideband Formatting

[0031]FIG. 4 shows vertical striping of wideband MPEG-TS packets 69 in a4-wide wideband channel 35. Wideband MPEG-TS packets 69 carry widebandDOCSIS data. Vertical Alignment Indexes (VAIs) increment across thehorizontal MPEG-TS packets 69. The VAI values in a vertical group ofwideband MPEG-TS packets are shown on the horizontal axis. For example,the wideband MPEG-TS packets 1-4 are assigned VAI values of 0.

[0032] The wideband channels are effectively independent of the layer-1physical layer (PHY) and operates as a shim between the PHY layer andthe layer-2 MAC layer. This allows the downstream bandwidth to benoncontiguous. The bandwidth assigned to a particular WCM can bedistributed in different noncontiguous portions of the the totalavailable RF spectrum. In other words, any selectable combination ofnon-contiguous RF channels can be used for any wideband channel.

[0033] The VAIs indicate a time sequence for the wideband MPEG-TSpackets 69 transmitted over the RF channels. The WCMs 34 use the VAIs torealign the wideband MPEG-TS packets 69 received from the WCMTS 28 overthe different RF channels. A Radio Frequency (RF) table (FIG. 17)identifies the frequencies for the RF channels and the order that theidentified RF channels should be decoded by the WCM 34.

[0034] The decoder 60 uses the VAI's to temporally align the widebandMPEG-TS packets 69 transmitted over the multiple RF channels. Thedecoder 60 then decodes particular RF channels in a particular channelsequence identified in the RF table (FIG. 17).

[0035] In the example shown in FIG. 4, the decoder 60 reads the widebandMPEG-TS packet 1 in RF channel 1 and then reads the wideband MPEG-TSpacket 2 in RF channel 2. The decoder 60 combines other wideband packets3, 4, 5, etc. from the RF channels in a similar manner. Different WCMs34 could scan different RF channel frequencies and in different RFchannel orders according to the sequence of frequencies contained in theRF table.

[0036]FIG. 5 shows the format of the wideband MPEG-TS packet 69 in moredetail. The wideband packet 69 consists of a MPEG-TS header 70, apointer field 72 (may not be present in all wideband packets), awideband header 74, and a DOCSIS payload 76. One example of fieldscontained in the standard MPEG-TS header 70 shown in Table 1.0.

[0037] A Packet Identifier (PID) exists in the current MPEG transportscheme. Particular PID values are used in a novel manner in oneembodiment of the present invention to identify payloads associated withwideband channels. The wideband PID values are used along with the RFtable by the WCMs 34 (FIG. 2) to decode wideband payloads that extendover multiple downstream channels.

[0038] A Continuity Counter (CC) is a prexisting field used in aconventional MPEG header. The CC is used in a novel manner in oneembodiment of the present invention for tracking wideband MPEG-TSpackets that extend over multiple RF channels.

[0039] The pointer_field 72 contains the number of bytes in the widebandpacket 69 that immediately follow the pointer_field 72 that the framer58 (FIG. 3) in the WCM 34 must skip before looking for the beginning ofa DOCSIS MAC frame. The pointer_field 72 may point to the beginning of aDOCSIS MAC frame. Alternatively, the pointer_field 72 may point to anystuff byte preceding the DOCSIS MAC frame. The pointer_field waspreviously used in DOCSIS to identify consecutive MPEG-TS packets in asame RF channel. The wideband scheme according to one embodiment of theinvention uses the pointer_field 72 to identify payloads that extendacross multiple RF channels. TABLE 1.0 MPEG-TS Header Format forWideband MPEG-TS packets Length Field (bits) Description sync_byte 8MPEG-TS packet Sync byte transport_error_(—) 1 Indicates an error hasoccurred in the indicator reception of the packet. This bit is reset tozero by the sender, and set to one by the receiver whenever an erroroccurs in transmission of the packet. payload_unit_(—) 1 A value of oneindicates the presence of a start_indicator pointer_field as the fifthbyte (PUSI) of the packet transport_priority 1 Reserved; set to zero PID13 Wideband channel packet identifier: transport_(—) 2 Reservedscrambling_(—) control adaptation_field_(—) 2 Use of theadaptation_field may not be control allowed on wideband channel PIDscontinuity_counter 4 Cyclic counter within a wideband channel (CC) PIDper RF channel

[0040] Table 2.0 shows the wideband header 74 in more detail. Thewideband header 74 contains reserved bits followed by the VerticalAlignment Index (VAI). The reserved field can be used to compensate forskew. For example, one of the RF channels may be substantially ahead ofthe other RF channels. The reserved field may be used to identify thesame VAI for two sequencial wideband MPEG-TS packets. The exact positionof the wideband header 74 within a wideband MPEG-TS packet 69 can varydepending on whether or not the pointer_field 72 is present. TABLE 2.0Wideband Header Format Length Field (bits) Description Reserved 2Reserved Vertical 6 A cyclic counter generated by the WCMTS AlignmentIndex conveys the vertical alignment of wideband MPEG-TS packets on allassociated RF channels.

[0041] The DOCSIS payload 76 in wideband MPEG-TS packet 69 can carryDOCSIS MAC frames and can also carry stuff bytes. The WCMTS 28 caninsert conventional MPEG-TS null packets or wideband MPEG-TS nullpackets in an inactive wideband channel. Unlike conventional MPEG-TSnull packets, wideband MPEG-TS null packets can provide VAIs to the WCMs34.

[0042] The DOCSIS MAC frames can begin anywhere within the payload 76 ofthe wideband MPEG-TS packet 69 and may span multiple wideband MPEG-TSpackets. Several DOCSIS MAC frames may exist within a single widebandMPEG-TS packet.

[0043]FIG. 6 shows a Payload Unit Start Indicator (PUSI) bit in theMPEG-TS header 70 that indicates the presence or absence of thepointer_field 72 as the first byte of the MPEG-TS payload. The start ofa DOCSIS MAC frame 78 in DOCSIS payload 76 is positioned immediatelyafter the wideband header 74. In FIG. 6, the pointer_field 72 is 1, andthe decoder 60 in the WCM 34 begins searching for a valid DOCSIS MACsublayer Frame Control (FC) immediately following the wideband header74.

[0044]FIG. 7 shows the case where a DOCSIS MAC frame 2 is preceded bythe tail of a previous DOCSIS MAC frame 1 and possibly a sequence ofstuff bytes 83. The pointer_field 72 identifies the first byte after thetail of frame I (which could be a stuff byte) as the position where thedecoder 60 in the WCM 34 should begin searching for a DOCSIS MACsublayer frame control value.

[0045]FIG. 8 shows multiple DOCSIS MAC frames 1, 2, and 3 containedwithin the same wideband MPEG-TS packet 69. The DOCSIS MAC frames mayfollow one after the other, or may be separated by an optional sequenceof stuff bytes 83. FIG. 9 shows the case where a DOCSIS MAC frame 1spans multiple wideband MPEG-TS packets 69A, 69B and 69C. The widebandMPEG-TS packet 69C encapsulates the start of the next MAC frame 2. Thepointer_field 72C for wideband packet 69C points to the byte followingthe last byte of the tail of MAC frame 1.

[0046] Wideband Dynamic Bandwidth Allocation

[0047]FIG. 10 shows how the bandwidth of the wideband channel can bedynamically adjusted by changing the number of RF channels. In oneexample, the wideband channel bandwidth is adjusted at wideband MPEG-TSpacket boundaries. The WCMTS 28 (FIG. 3) can dynamically vary thebandwidth of multiple different wideband channels simply by varying thewideband configuration parameters in the RF table associated withdifferent PIDs.

[0048] For example, FIG. 10 shows three wideband channels PID=X, Y, andZ mapped over four RF channels 1-4. The three wideband channels areconfigured using a RF channel frequency tables. The RF channel frequencytable is part of the wideband channel descriptors that specify widebandchannels as entering over RF channels 1-4. The channel frequency tableis part of the wideband channel descriptor 55 shown in FIG. 17.

[0049] Pursuant to the RF frequency table, the WCM 34 finds the widebanddata by monitoring all four RF channels 1-4 for wideband packets havingcertain PID values (See Table 1.0). The WCM 34 further filters thewideband channel data by looking for MAC addresses in the DestinationAddress (DA) field of the Ethernet packets in the DOCSIS MAC framepayloads within the wideband channel.

[0050]FIG. 10 shows a wideband channel PID=X that uses the entirebandwidth of all four RF channels 1, 2, 3, and 4 when the widebandMPEG-TS packets 69 have Vertical Alignment Indexes (VAI) equal to N. Forthe next wideband MPEG-TS packets transported at VAI=N+1, RF channels 1and 2 carry wideband channel PID=Y and RF channels 3 and 4 continue tocarry wideband channel PID=X. The equal division of bandwidth betweenwideband channels X and Y continues until the wideband MPEG-TS packetshave VAIs equal to M+1.

[0051] At VAI=M+1, wideband channel X again utilizes the entirebandwidth of all four RF channels. This RF channel utilization continuesup to and including when the transported wideband MPEG-TS packets haveVAIs equal to P. When the next wideband MPEG-TS packets are transportedat VAI=P+1, RF channels 2-4 are used for wideband channel Z while RFchannel 1 is used for wideband channel X.

[0052] The WCM decoder 60 reads the PID values in each wideband packet69. Since all wideband packets for VAI=N have the same PID value, theWCM decoder 60 combines these packets together as part of the samewideband channel. At VAI=N+1, the wideband packets for RF channels 1 and2 have PID=Y and the RF channels 3 and 4 have PID=X. The WCM decoder 60by reading the PIDs knows to combine the MPEG frames, if appropriate,for wideband channel X in the RF channels 3 and 4 with other MPEG framespreviousely received in RF channels 1-4 for wideband channel X at VAI=1.The WCM decoder 60 similarly combines when appropriate the MPEG framesreceived in wideband channel Y over RF channels 1 and 2 for VAI=N+1through VAI=M.

[0053]FIG. 11 shows how the Vertical Alignment Indexes (VAIs) operate incombination with Continuity Counters (CCs). The CC is a fieldincremented with each transport stream packet having the same PacketIdentifier (PID). In one example, seventeen wideband MPEG-TS packetslots VAI=0 through VAI=16 are transmitted over each of four RFchannels. Two wideband channels X and Y are mapped over the four RFchannels 1, 2, 3 and 4.

[0054] The VAT values are used for aligning vertical groups of widebandMPEG-TS packets across all the RF channels. The CC values incrementhorizontally across RF channels according to the wideband channel. TheCCs in wideband MPEG-TS packets are treated independently for each RFchannel PID. This allows the WCM decoder 60 to determine which widebandpackets in a sequence for a particular RF channel have been received,even when wideband packets for a particular wideband channel are nottransmitted for certain VAI packet slots.

[0055]FIG. 12 shows six fiber nodes A-F, each with a separate forwardcarrier path. Each forward carrier path contains its own RF spectrum.The wideband channels WB1-WB4 are associated with the RF channels 1-4and the narrow band channels NB1-NB4 are associated with RF channel 5.Fiber nodes A and B each share the same narrowband channel NB1 andwideband channel WB1. This results in a single association of WB1 toNB1. It should be understood that this is only one example, and anycombination of any number of wideband and narrowband channels can beassociated with any number and combination of RF channels.

[0056] Fiber nodes C and D share wideband channel WB2 and each havetheir own narrowband channels NB2 and NB3, respectively. This results intwo separate associations of WB2 to NB2, and WB2 to NB3. Fiber nodes Eand F share the same narrowband channel NB4, but have different widebandchannels WB3 and WB4, respectively. This results in two separateassociations of WB3 to NB4 and WB4 to NB4. In one embodiment, there isone PID assocaited with each wideband channel. The wideband channeldescriptors associated with a particular PID then identify to the WCMsof the RF channels and sequence associated with the wideband channelsand narrowband channels.

[0057] The wideband channel descriptor 55 (FIG. 3) is sent by the WCMTS28 over the narrowband channel 30A. The WCD 55 contains channeldescriptors that identify the RF channel frequencies, sequence, and PIDsfor the wideband channels associated with each fiber node A-F. Eachunique association of wideband channel to narrowband channel may haveits own wideband channel descriptor.

[0058] Interleaving Wideband and Narrowband Channels

[0059] Narrowband and wideband cable modems can receive narrowbandMPEG-TS packets over either an RF channel dedicated to a narrowbandchannel, or an RF channel where wideband and narrowband channels areinterleaved. FIGS. 13 and 14 illustrate two differnet scenarios.

[0060]FIG. 13 shows five RF channels 1-5. RF channels 1-4 carry widebandMPEG-TS packets 90 for wideband channel X. The RF channel 5 carriesnarrowband MPEG-TS packets 92 in a narrowband channel (PID=DOCSIS PID).The wideband packets 90 from RF channels 1-4 are combined together bythe WCM 34 to generate a single wideband data stream. The narrowbandpackets 92 from RF channel 5 are combined together to generated a singlenarrowband data stream.

[0061]FIG. 14 shows another interleaving configuration where RF channels1-4 carry both wideband and narrowband channels. The wideband channel Xextends over different combinations of all four RF channels 1-4 and thenarrowband channel (PID=DOCSIS PID) is interleaved with the widebandchannel X on RF channel 4.

[0062] The bandwidth of wideband channel X can be dynamically adjustedto allow the narrowband channel 92 to share the bandwidth of RF channel4 during the packet slots from VAI=N+1 through VAI=M. The WCMs 34 (FIG.3) are configured using the WCD 55 (FIG. 17) to receive wideband channelX over RF channels 1-4. The WCM decoder 60 identifies the narrowbandpacket 92 at VAI=N+1 by detecting PID=DOCSIS PID in the MPEG-TS header.The WCM decoder 60 processes the narrowband packet 92 as a conventionalsingle band DOCSIS MPEG-TS packet by combining packet 92 with othernarrowband packets identified (PID=DOCSIS PID) on RF channel 4.

[0063]FIG. 15 is an example showing how DOCSIS MAC frames span multiplewideband MPEG-TS packets 98 even when the wideband channel bandwidthdynamically changes. In this example, two wideband channels PID=X andPID=Y and a narrowband channel 94 are interleaved across four RFchannels 1-4. The wideband channel descriptor in FIG. 17 identifies theRF channels 1-4 associated with wideband channels X and Y.

[0064] The first three wideband MPEG-TS packets transmitted on RFchannels 1-3 have VAI=0 and PID=X. The RF channel 4 at VAI=0 has aPID=DOCSIS PID. At VAI=1, RF channels 1 and 2 have. PID=Y. The widebandMPEG-TS packets for RF channels 3 and 4 at VAI=1 have PID=X. NarrowbandMPEG-TS packets do not contain a VAI field. The values of the ContinuityCounters (CCs) in the first four vertical MPEG-TS packets arearbitrarily chosen to illustrate the independence of CCs between RFchannels.

[0065] The decoders 60 in the WCMs 34 conduct the following widebandstriping sequence according to the above VAI and PID values. The DOCSISMAC frame X1 begins inside the wideband MPEG-TS packet 98 with VAI=0 onRF channel 1. The PID value of X in the MPEG-TS header 96 identifies thewideband MPEG-TS packet 98 as part of wideband channel X. The widebandMPEG-TS packet 98 has a Payload Unit Start Indicator (PUSI) bit in theMPEG-TS header 96 set to 1, indicating that the pointer_field ispresent. The pointer_field points to one of the stuff bytes 97 precedingthe beginning of DOCSIS MAC frame X1.

[0066] The DOCSIS MAC frame X1 continues in the wideband MPEG-TS packet100 on RF channel 2 at VAI=0. The entire payload of the wideband MPEG-TSpacket 100 contains the continuation of DOCSIS MAC frame X1 from RFchannel 1. The PUSI bit is accordingly set to 0 and there is nopointer_field. In one embodiment, stuff bytes are only inserted betweenDOCSIS MAC frames, therefore no stuff bytes exist in wideband MPEG-TSpacket 100.

[0067] The DOCSIS MAC frame X1 ends on the wideband MPEG-TS packet 102on RF channel 3 at VAI=0. The DOCSIS MAC frame X1 is immediatelyfollowed by DOCSIS MAC frame X2. The DOCSIS MAC frame X2 is a smallframe totally contained in wideband MPEG-TS packet 102. Thepointer_field 106 is used in wideband packet 102 to point to thebeginning of new DOCSIS MAC frame X2. The DOCSIS MAC frame X2 isfollowed by optional stuff bytes 108 and the beginning of DOCSIS MACframe X3. Although wideband MPEG-TS packet 102 contains the beginning oftwo DOCSIS MAC frames X2 and X3, the pointer_field points to the firstnew MAC frame X2.

[0068] The narrowband MPEG-TS packet on RF channel 4 and the widebandMPEG-TS packets with VAI=1 on RF channels 1 and 2 do not have a PIDvalue of X. The DOCSIS MAC frame X3 accordingly is continued on the nextwideband MPEG-TS packet 104 with VAI=1 and PID=X on RF channel 3. TheDOCSIS MAC frame X3 ends in the wideband MPEG-TS packet 110 on RFchannel 4 having VAI =1. The DOCSIS MAC frame X3 in wideband packet 110is followed by a number of stuff bytes 114 and the start of DOCSIS MACframe X4. The pointer_field 112 in wideband MPEG-TS packet 110 points tothe beginning of DOCSIS MAC frame X4. Alternatively, the pointer_field112 could point to any of the preceding stuff bytes 114.

[0069] MPEG over MPEG Byte Striping

[0070]FIG. 16 shows one alternative embodiment referred to as verticalbyte striping. Referring to FIGS. 3 and 16, a wideband transport channel120 is created by vertically byte-striping MPEG-TS packets over multiplehorizontal MPEG-TS streams. At the physical layer, each RF channel 1-4runs independently as a separate MPEG-TS stream. At the link layer, thewideband transmitter 44 aligns the various RF channels 1-4 that make upa wideband transport sub-channel by selecting values in the PID field inMPEG-TS header 125. The wideband decoder 60 in FIG. 3 corrects forjitter in the RF channels 1-4 between the wideband transmitter 44 andwideband receiver 58 using the VAI values 124 to realign the horizontalMPEG-TS streams. The receiving WCMs 34 recreate the original MPEG-TSstream by de-striping the vertical MPEG-TS stream from the horizontalMPEG-TS streams.

[0071] The wideband channel 120 can be run as a single fat widebandtransport sub-channel, sub-divided into several smaller widebandtransport sub-channels, or run as a mixture of wideband transportsub-channels and narrowband channels. In FIG. 16, during the firsthorizontal MPEG-TS packet time, RF channels 1, 2 and 3 are run as a3-wide wideband transport channel, while RF channel 4 is run as anarrowband channel.

[0072] The PID field in the MPEG packet header 125 indicates which RFchannels are being used to stripe the wideband data for a given widebandtransport sub-channel. The PID is set to the value of X for the widebandtransport sub-channel. The PID value X can be any value except reservedvalues (e.g. 0×1FFFE). In this example, the WCMTS 28 knows that there isa 4-channel wide wideband receiver 58 listening on the four RF channels1-4.

[0073] The WCMTS 28 may decide that it needs to use three of the four RFchannels to keep up with Quality of Service (QoS) bandwidthrequirements. Accordingly, the WCMTS 28 transmits with the PID set to Xover RF channels 1, 2, and 3. During the next MPEG-TS packet time, theWCMTS 28 may decide that it only needs two RF channels worth ofbandwidth and transmits with a PID set to X only over RF channels 3 and4.

[0074] The WCM 34 looks on the four RF channels 1-4 for widebandchannels with a PID=X and de-stripes the wideband data from all MPEG-TSpackets having a PID=X. If another wideband channel PID value isdetected, the WCM 34 combines that wideband packet with other widebandpackets having a similar PID value.

[0075] This dynamic channel assignment allows the WCMTS 28 to balancethe load between all the subscribers by simply choosing which and howmany RF channels to stripe the wideband transport sub-channel for anygiven time slot. The WCMTS 28 does not need to notify the WCM a priori,as the PID information is sent in-band and is sufficient for the WCM 34to adjust the received channels dynamically to keep up with the WCMTStransmission.

[0076] Wideband Channel Descriptor (WCD)

[0077]FIGS. 17 and 18 show how a Wideband Channel Descriptor (WCD) 55 istransmitted by a wideband capable CMTS 28 at periodic intervals todefine the characteristics of a logical wideband downstream channel. Aseparate message may be transmitted for each logical wideband downstreamchannel that is currently available for use. The CMTS 28 generates WCDs55 that contain the information shown in FIG. 17.

[0078] A configuration change count is incremented by one by the CMTS 28whenever any of the values of the channel descriptors in WCD 55 change.If the value of the count in a subsequent WCD 55 remains the same, theWCMs 34 can quickly decide that the channel operating parameters havenot changed, and may be able to disregard the remainder of the message.

[0079] The WCD 55 includes a MAC management header 130, a transaction ID132 and TLVs 134 containing wideband configuration data 134 thatspecifies how PID 136 is used in the wideband packet header to identifythe wideband channel. The TLVs 134 specifies in field 140 the number ofphysical RF channels used to carry the wideband channel and identifiesin field 138 narrowband downstream channels associated with the widebandchannel. The TLVs 134 can include the RF table 142 that contains asequence number 144 indicating what order the RF channel payloads aredecoded by the WCMs. Center frequencies 146 indicate the frequences foreach RF channel used in the wideband channel. The RF channels may besequenced in any order and may or may not be adjacent in frequency toeach other.

[0080] The WCMTS 28 and WCM 34 can support data link encryption withinthe wideband channels. The WCMTS 28 may or may not use the sameencryption and keying for the WCM 34 used on the associated narrowbandchannel. The cable modems can accept the same keying on both thenarrowband channel and with wideband channel, or can accept separatekeying for wideband and narrowband channels.

[0081] Wideband Channel Acquisition

[0082]FIG. 18 shows how the WCM 34 acquires a logical wideband channel.The WCM 34 first acquires a DOCSIS narrowband channel 130A and completesranging making an upstream channel 132 operational. The WCMTS 28 assignsa PID value to the WCM 34 and downloads the WCD 55 containing thewideband channel parameters including the frequency table 142 to the WCM34.

[0083] The WCM 34 reads the wideband channel descriptors 55 having theassigned PID 136 (FIG. 17). The WCM 34 issues a REG-REQ 134 to the WCMTS28 along with any WCD wideband capabilities parameters 136. After theWCM 34 receives an REG-RSP 138 back from the WCMTS 28, all downstream RFchannels 130A-130N are acquired that are identified as comprising thewideband channel. A REG-ACK 140 is sent from the WCM 34 back to theWCMTS 28. The WCM 34 then starts receiving data on the assigned widebandPID.

[0084] The WCMTS 28 can periodically reassign different widebandperameters to one or more of the wideband cable modems 34. For example,the WCMTS 28 may send a wideband channel descriptor 55 to a WCM 34 listsa first set of RF channels in a first sequence for the WCM's widebandchannel. Some time later, the WCMTS 28 may send another wideband channeldesciptor 55 having the same associated PID value but that contains adifferent set of RF channels to be used as wideband or narrowbandchannels or that lists the same set of RF channels in a different order.

[0085] The WCMTS 28 can use the wideband channel descriptors 55 todynamically send different wideband configuration data to particularWCMs 34 based on changing bandwidth requirements. For example, atdifferent times there can be different wideband and narrowband payloaddemands. The WCMTS 28 uses the wideband channel descriptor 55 todynamically reassign the RF channels to different wideband andnarrowband channels according to these changing bandwidth demands.

[0086] The dynamic assignment of RF channels can also be used toincrease system reliability. For example, the WCMTS or WCM may identifyfaults in one or more RF channels. The WCMTS can then send a widebandchannel descriptor 55 containing a new RF table to the WCMs using the RFchannels identified with faults. The new RF table dynamically drops theidentifed RF channels from the wideband or narrowband channels.

[0087] A CM without wideband capabilities may not recognize any of thenew wideband-specific TLVs 134 in the WCD 55. The CM may be unable toregister successfully if provisioned with the WCD 55 that containswideband-specific parameters. When interoperating with a CM that doesnot have wideband-specific capabilities, the WCMTS 28 would allow a CMto register and operate as a CM. When WCM 34 registers with the WCMTS28, the WCMTS 28 may return the REG-RESP message 138 that configures theWCM 34 in a mode with or without wideband-specific capabilities.

[0088] When interoperating with a WCMTS 28, a CM withoutwideband-specific capabilities receives data on a single RF channel130A. When interoperating with a CMTS without wideband-specificcapabilities, a WCM 34 receives data on a single RF channel 130A.

[0089] Packet Skew Wideband MPEG-TS packet skew is defined to be themaximum expected skew from the arrival of the first MPEG-TS packet witha given VAI to the arrival of the last MPEG-TS packet with the same VAIwithin a given wideband channel. The skew is measured at the WCMreceiver MAC interface to the PHY.

[0090] The MPEG-TS packets that make up a wideband channel are de-skewedusing the VAI in the wideband MPEG header 74 (FIGS. 6-9). The MPEG-TSpackets with PID values other than those defined to be wideband PIDs,including narrowband packets (PID=DOCSIS PID) and MPEG-TS nulls, willnot contain valid VAIs. If the WCM 34 does not receive an MPEG-TS packetfor a given VAI within the specified maximum skew window for any givenRF channel of the wideband channel, the WCM 34 concludes no widebandMPEG-TS packet was sent on that RF channel for the given VAI.

[0091] Alternatively, the next consecutive CC for that PID may bereceived in another VAI packet slot. The WCM 34 may then conclude thatno wideband packet for that PID was sent in the previous VAI packetslot.

[0092] The system described above can use dedicated processor systems,micro controllers, programmable logic devices, or microprocessors thatperform some or all of the operations. Some of the operations describedabove may be implemented in software and other operations may beimplemented in hardware.

[0093] For the sake of convenience, the operations are described asvarious interconnected functional blocks or distinct software modules.This is not necessary, however, and there may be cases where thesefunctional blocks or modules are equivalently aggregated into a singlelogic device, program or operation with unclear boundaries. In anyevent, the functional blocks and software modules or features of theflexible interface can be implemented by themselves, or in combinationwith other operations in either hardware or software.

[0094] Having described and illustrated the principles of the inventionin a preferred embodiment thereof, it should be apparent that theinvention may be modified in arrangement and detail without departingfrom such principles. I claim all modifications and variation comingwithin the spirit and scope of the following claims.

1. A wideband cable modem, comprising: a receiver configured to receiveand decode one or more logical wideband channels that extend overmultiple downstream channels.
 2. A wideband cable modem according toclaim 1 wherein the wideband channels contain wideband packets havingVertical Alignment Indexes (VAIs), the receiver using the VAIs totemporally realign the wideband packets received over the differentdownstream channels.
 3. The wideband cable modem according to claim 1wherein the receiver includes multiple tuners having demodulators eachdemodulating a different one of the multiple downstream channels.
 4. Thewideband cable modem according to claim 3 wherein the demodulators areQuadrature Amplitude Demodulators.
 5. The wideband cable modem accordingto claim 1 including a decoder that identifies and decodes the widebandchannels into data streams.
 6. The wideband cable modem according toclaim 5 wherein the decoder identifies associated wideband channelsaccording to packet identifiers in wideband packet headers.
 7. Thewideband cable modem according to claim 1 wherein the receiverdynamically uses different combinations of the downstream channels fordecoding the wideband channel according to a received wideband channeldescriptor.
 8. The wideband cable modem according to claim 1 wherein thesame downstream channels for decoding both wideband and narrowbandchannels.
 9. The wideband cable modem according to claim 1 wherein thewideband channels are established using a Data Over Cable ServiceInterface Specifications (DOCSIS) protocol.
 10. The wideband cable modemaccording to claim 1 wherein one of the wideband channels comprisewideband packets having a MPEG header, a wideband header and a Data OverCable Service Interface Specification (DOCSIS) payload that containsMedia Access Control (MAC) frames.
 11. The wideband cable modemaccording to claim 1 wherein the wideband channels are formed withwideband packets that are received over different ones of the downstreamchannels.
 12. The wideband cable modem according to claim 11 includingMedia Access Control (MAC) frames contained in wideband packet payloads,the MAC frames extending over multiple wideband packets received ondifferent downstream channels.
 13. A wideband cable modem terminationsystem, comprising: a transmitter configured to decompose a data streaminto wideband packets that form wideband channels extending overmultiple Radio Frequency (RF) channels.
 14. A wideband cable modemtermination system according to claim 13 including multiple modulatorsconfigured to modulate the wideband packets on the multiple RF channels.15. A wideband cable modem termination system according to claim 13wherein the transmitter generates a wideband channel descriptor thatidentifies which RF channels are used for transmitting the widebandchannel.
 16. A wideband cable modem termination system according toclaim 15 wherein the wideband channel descriptor identifies a sequencefor decoding the RF channels used for transmitting the wideband packets.17. A wideband cable modem termination system according to claim 15wherein the transmitter dynamically changes the RF channels used fortransmitting the wideband channel by transmitting another widebandchannel descriptor that identifies different RF channels.
 18. A widebandcable modem termination system according to claim 15 wherein thetransmitter sends the wideband channel descriptor message to cablemodems using a Data Over Cable Service Interface Specification (DOCSIS)communication protocol.
 19. A wideband cable modem termination systemaccording to claim 13 wherein the transmitter uses packet identifiers toassociate the wideband packets with the wideband channels.
 20. Awideband cable modem termination system according to claim 19 whereinthe transmitter locates the packet identifiers in a Moving PictureExperts Group (MPEG) packet header.
 21. A wideband cable modemtermination system according to claim 13 wherein the transmitterincludes a pointer field in the wideband packets to identify MediaAccess Control (MAC) frames in the wideband packets.
 22. A widebandcable modem termination system according to claim 13 wherein thetransmitter includes Vertical Alignment Indexes (VAIs) in the widebandpackets to identify temporal positions of the wideband packets in themultiple RF channels.
 23. A wideband cable modem termination systemaccording to claim 13 wherein the transmitter includes continuitycounters in the wideband packets that identify what sequence thewideband packets for the same wideband channel are transmitted on thesame RF channels.
 24. A wideband cable modem termination systemaccording to claim 13 wherein the transmitter establishes widebandchannels and narrowband channels over the multiple RF channels at thesame time.
 25. A wideband cable modem termination system according toclaim 14 wherein the transmitter dynamically reconfigures the widebandchannels and the narrowband channels over different combinations of themultiple RF channels during a same transmission session.
 26. A methodfor transferring data over a cable network, comprising: encoding a datastream into wideband packets; associating the wideband packets with awideband channel that uses multiple RF channels; and transmitting thewideband packets over the multiple RF channels of the wideband channel.27. A method according to claim 26 including changing bandwidth of thewideband channel by dynamically varying a number of the RF channels usedfor transmitting the wideband packets.
 28. A method according to claim26 including: identifying a new data stream for transmitting over a newwideband channel; dynamically changing the number of RF channels usedfor transmitting the wideband channel to accommodate the new widebandchannel.
 29. A method according to claim 26 including transmitting oneor more narrow band channels with the wideband channel on the RFchannels.
 30. A method according to claim 26 including assigning packetidentification values to the wideband packets associating the widebandpackets with different wideband channels.
 31. A method according toclaim 26 including assigning continuity values to the wideband packetsthat identify an order that the wideband packets are transmitted overthe different cable channels.
 32. A method according to claim 26including sending a wideband channel descriptor message indicating whichRF channel frequencies are used in the wideband channels.
 33. A methodaccording to claim 26 including using a field in a Motion PicturesExperts Group (MPEG) packet header to identify the wideband packets. 34.A method according to claim 26 including: transmitting a widebandchannel descriptor that identifies a set of RF channels used in thewideband channel.
 35. A method according to claim 34 includingdynamically changing which RF channels are used in the wideband channelby transmitting a new wideband channel descriptor that identifies adifferent set of RF channels.
 36. A method according to claim 34including sending a channel sequence in the wideband channel descriptoridentifying a sequence for decoding RF channels for the widebandchannel.
 37. A method according to claim 37 including sending a widebandchannel descriptor that changes the channel sequence.
 38. A method fortransferring data over a cable network, comprising: encoding a datastream into wideband packets; associating the wideband packets with awideband channel that includes multiple RF channels; transmitting thewideband packets over the multiple RF channels of the wideband channel;and dynamically varying the RF channels used for transmitting thewideband channel.
 39. A method according to claim 38 including:detecting a fault condition in one or more of the RF channels used forthe wideband channel; and dynamically dropping the RF channels with thedetected fault condition from the wideband channel.
 40. A methodaccording to claim 38 including: encoding different data streams intowideband packets; assigning the wideband packets for the different datastreams to different wideband channels; assigning different combinationsof the RF channels to the wideband channels; transmitting the widebandpackets over the RF channels for the assigned wideband channels.
 41. Amethod according to claim 38 including transmitting different widebandand narrowband channels over the same RF channels at the same time. 42.A method according to claim 41 including dynamically varying which RFchannels are used for the wideband channels and the narrowband channels.